1. Field of the Invention
The present invention relates to an air-intake apparatus of a multi-cylinder internal combustion engine having an intake air control valve for controlling intake air suctioned into combustion chambers of respective cylinders of the engine. Specifically, the present invention relates to an air-intake apparatus of an internal combustion engine that generates rotational flows (intake air vortex flows) in combustion chambers of respective cylinders of the engine to improve combustion efficiency.
2. Description of Related Art
Conventionally, there has been known an air-intake apparatus of an internal combustion engine having a tumble flow control valve (TCV) and a variable intake air control valve (ACISV). The tumble flow control valve generates a tumble flow in a longitudinal direction in a combustion chamber of each cylinder of the internal combustion engine (four-cylinder engine) to improve combustion efficiency in the combustion chamber. Thus, improvement of fuel consumption or emission (e.g., HC reduction effect) is aimed. The variable intake air control valve varies intake passage length (intake pipe length) of the four-cylinder engine to effectively utilize an inertial supercharging effect, thereby improving an output of the four-cylinder engine (for example, refer to Patent document 1: JP-A-2006-161885).
The tumble flow control valve has four valves as valve members, a single shaft for supporting the valves, multiple bushings for rotatably supporting the shaft, and the like.
As shown in FIGS. 13A and 13B, the variable intake air control valve has four valves 102 for opening and closing multiple intake passages formed in an intake manifold 101 respectively, a shaft 103 for supporting and fixing the valves 102, multiple shaft bushings for rotatably supporting the shaft 103, and the like.
The shaft 103 has an annular protrusion 104 (i.e., annular flange) protruding radially in the shape of a flange.
The shaft bushing is composed of a fixed bushing half body 111 and a movable bushing half body 112. The fixed bushing half body 111 is fixed to the intake manifold 101. The movable bushing half body 112 rotatably supports the shaft 103 in combination with the fixed bushing half body 111. The movable bushing half body 112 is provided such that the movable bushing half body 112 can be displaced freely in the radial direction of the shaft 103. Annular grooves 113, 114 for accommodating the annular protrusion 104 are formed in the fixed bushing half body 111 and the movable bushing half body 112.
The shaft bushing described in Patent document 1 supports the shaft 103 such that the shaft 103 can rotate smoothly. At the same time, the annular protrusion 104 of the shaft 103 restricts displacement of the shaft 103 in a thrust direction in combination with the annular grooves 113, 114 of the fixed bushing half body 111 and the movable bushing half body 112.
The air-intake apparatus of the internal combustion engine described in Patent document 1 is assembled by loosely inserting the annular protrusion 104 of the shaft 103 into the annular grooves 113, 114 of the shaft bushing (fixed bushing half body 111 and movable bushing half body 112). Therefore, backlash arises in the thrust direction of the shaft 103 inevitably.
A clearance (e.g., side clearance) is formed between a passage wall surface of the intake manifold 101 and a side surface (outer peripheral surface) of each valve 102 in order to suppress increase of sliding resistance (sliding torque) of the valve 102. There is a possibility that a dimensional change arises in the clearance because of a difference between linear expansion coefficients of the intake manifold 101 and the shaft 103, i.e., because of temperature change. Accordingly, galling or friction can arise between the passage wall surface of the intake manifold 101 and the side surface (outer peripheral surface) of the valve 102. As a result, there can occur a problem that the intake manifold 101 and the valves 102 wear or generate a hammering sound (abnormal noise).
There is a possibility that backlash occurs in a rotational axis direction (i.e., thrust direction) of the shaft 103, which links the multiple valves 102 such that the valves 102 can move in conjunction with each other. Therefore, positions of the four valves 102, which are arranged for the respective cylinders of the four-cylinder engine correspondingly, in the thrust direction cannot be decided correctly. Accordingly, when the four valves 102 are fully closed, a variation arises among flow rates of leak air passing through clearances (gaps) on both sides of the valves 102 with respect to the rotational axis direction. Therefore, there is a problem that aimed performance (i.e., effect to improve engine output) cannot be achieved.
When the shaft bushing (fixed bushing half body 111 and movable bushing half body 112) described in Patent document 1 is applied to a tumble flow control valve, a variation arises among flow rates of leak air flowing from circumferences of the valves. Accordingly, generation of the rotational flows (tumble flows) in the combustion chambers of the four-cylinder engine becomes unstable. Therefore, there is a problem that aimed performance (e.g., effect to improve combustion efficiency of four-cylinder engine or effect to improve fuel consumption through stabilization of combustion) cannot be achieved.